The invention relates to a method for ascertaining the restarting capability of a vehicle when parking the vehicle, and to a pressure vessel system for a vehicle.
In pressure vessel systems for CGH2 and CNG in vehicles known to date, the pressure of the fuel in the pressure vessel drops due to the extraction of hydrogen. At a certain limit pressure, for example 20 bar, further extraction is usually no longer possible or no longer permissible in order to prevent deformation or buckling of the pressure vessel owing to a further drop in pressure due to further extraction of fuel. In addition, the fuel typically has to have a minimum pressure, so that the fuel passes from the pressure vessel to the fuel consuming apparatus by means of which the vehicle is driven.
The operation of the vehicle may result in cooling down of the fuel due to extraction (expansion chill) in specific situations, for example high installation space temperature (the installation space temperature is the temperature which prevails in the installation space of the pressure vessel) and low extraction rate, on account of the installation space temperature (exhaust gas system and waste heat from the fuel consuming apparatus) being compensated and, as a result, the fuel in the pressure vessel being at a temperature which is equal to or greater than the ambient temperature when parking the vehicle or during planned restarting of the vehicle (the ambient temperature is the outside temperature). This state can theoretically occur in winter when the pressure vessel or the tank is heated by the vehicle waste heat during the extraction phase and cools down when parked overnight.
Therefore, in the case of pressure vessel systems known to date, the situation can occur under unfavorable circumstances (for example due to very large day/night temperature differences, extreme weather fluctuations) of there being a sufficiently high pressure (greater than the minimum pressure value) of the fuel in the pressure vessel before parking the vehicle and turning off the vehicle, but the pressure of the fuel dropping below the minimum pressure value as a result of cooling down due to the surroundings while the vehicle is parked and, respectively, switched off, as a result of which the vehicle can no longer be started.
Consequently, under unfavorable circumstances, it can occur that the pressure of the fuel lies above the minimum pressure value or a minimum pressure before the vehicle is parked but the vehicle no longer has the capability to start after parking since the pressure of the fuel in the pressure vessel is too low even though there is a sufficient quantity of fuel in the pressure vessel for driving the vehicle. This statement applies only when the temperature of the medium rises (due to rising ambient temperature).
High-pressure gas vessel systems (also called “CGH2 systems”) are designed to permanently store fuel at a pressure of over approximately 350 bar overpressure (=overpressure in comparison to atmospheric pressure), further preferably of over approximately 500 bar overpressure and particularly preferably of over approximately 700 bar overpressure, at ambient temperatures.
Cryogenic pressure vessel systems (also called “CcH2 systems”) are known from the prior art. By way of example, EP 1 546 601 B1 discloses a system of this kind.
It is a preferred object of the technology disclosed here to reduce or to eliminate at least some disadvantages of the previously known solutions. Further preferred objects can be found in the advantageous effects of the technology disclosed here.
In particular, the object is achieved by a method for ascertaining the restarting capability of a vehicle, in particular when parking the vehicle, wherein the vehicle has a pressure vessel system comprising a pressure vessel for storing a fuel, the method comprising the following steps: detecting the pressure and the temperature of the fuel in the pressure vessel, determining a final pressure value of the fuel in the pressure vessel, wherein the final pressure value is the expected pressure of the fuel in the pressure vessel after a parking period of the vehicle, comparing the determined final pressure value with a minimum pressure value for ascertaining whether the vehicle is capable of restarting after the parking period, and generating a notification signal when the determined final pressure value is lower than the minimum pressure value.
One advantage of this is that it is ascertained whether the vehicle can be restarted before parking the vehicle, in particular when parking the vehicle. As a result, possible breakdown of the vehicle after parking is prevented. The expected pressure of the fuel in the pressure vessel is, in particular, the calculated or estimated pressure of the fuel in the pressure vessel. The calculation or estimation can take place, in particular, on the basis of the respectively current known values.
The parking period or the period for which the vehicle is turned off can be entered by the user or driver or can be a calculated parking period based on experience or historical data. It is possible to estimate or determine, on the basis of the time of day and the location (for example 23:00 hours, at the home address of the driver), how long the parking period is likely to be (for example approximately 8 hours until the driver drives from the home address to his/her place of work the next morning).
The term “during parking” can include the time period shortly before the vehicle is actually parked (for example when entering a parking spot or when driving into a parking garage or underground parking garage). Ascertaining whether parking is immediately imminent or currently taking place can be carried out on the basis of position data, historical data and/or by a parking button which the driver operates. The term “before parking” also includes the time during driving of the vehicle. Therefore, the minimum pressure value can be determined again at intervals or continuously during driving or operation of the vehicle.
The vehicle is no longer capable of starting when the pressure of the fuel at the end of the parking period is below the minimum pressure value since the supply pressure for the fuel cell is too low or further extraction of fuel from the pressure vessel can lead to damage to the pressure vessel.
The ambient temperature can be taken into account when determining the final pressure value. By taking into account the ambient temperature or outside temperature, it is possible to predict more precisely whether the vehicle can be restarted after parking. Consequently, even smaller quantities of fuel may be sufficient for restarting the vehicle after parking.
The expected temperature development of the ambient temperature during the parking period, in particular on the basis of weather forecast data, can be taken into account when determining the final pressure value. As a result, it is possible to predict more reliably whether the vehicle can be restarted after parking. Therefore, even smaller quantities of fuel may be sufficient for restarting the vehicle after parking, e.g., because the fuel cell in park mode has converted H2. It is important that the medium temperature in this case is higher than when parking.
A notification to the driver of the vehicle, in particular a warning notification to the driver of the vehicle that the vehicle should not be parked but rather the pressure vessel of the vehicle should be filled before parking, is given on the basis of the notification signal. As a result, the driver of the vehicle can take measures in order to ensure a restarting capability of the vehicle after parking. In particular, the driver can fill the pressure vessel system with fuel before parking, so that restarting of the vehicle after parking will be possible. It is also conceivable for the driver to park the vehicle in a parking garage or in a manner protected against cold, so that the temperature of the fuel and consequently the pressure of the fuel does not drop so severely.
In response to the notification signal being generated, the fuel in the pressure vessel can be heated and the final pressure value can be determined again until the final pressure value has reached or undershot the minimum pressure value if it is possible to reach the minimum pressure value without exceeding a maximum temperature of the fuel in the pressure vessel and without exceeding a maximum pressure of the pressure vessel solely by heating. One advantage of this is that it is actively ensured that, when restarting of the vehicle after the parking period or after parking is actually possible on the basis of the existing quantity of fuel or density of fuel, adequate pressure conditions for restarting the vehicle are generated before parking, in particular when parking the vehicle. This prevents breakdown of the vehicle.
The minimum pressure value can be determined depending on the range of the vehicle which is required until the next filling station for filling the pressure vessel. The minimum pressure value is therefore determined (at a high level) in such a way that there is a sufficiently high pressure in the pressure vessel even while fuel is being consumed on the way to the next filling station (after parking and restarting of the vehicle). “Sufficiently high” means, in particular, that (even while driving directly to the nearest filling station after parking) neither is the supply pressure for the fuel cell, or will the supply pressure for the fuel cell become, too low nor can further extraction of fuel from the pressure vessel lead to damage to the pressure vessel. The minimum pressure value which is determined in this way is therefore higher than the minimum pressure value which is determined when the range which is required until the next filling station is not taken into consideration but rather the focus is only on restarting the vehicle after parking. One advantage of this is that not only is it ensured that the vehicle is capable of restarting after parking but a check is also made as to whether the vehicle has a sufficiently high pressure to move the vehicle to the next filling installation or filling station after restarting the vehicle after parking. Consequently, a check is made as to whether it (is expected that it) will be possible to drive to the next filling station after parking. The minimum pressure value can be determined again during driving (and therefore before parking the vehicle) at intervals or continuously. In this case, the starting point can be, for example, a parking period which is of such a length that the temperature of the fuel has reached the temperature of the surroundings (in particular the ambient temperature after the parking period) (thermodynamic equalization). As an alternative, the parking period can be estimated, for example, with reference to historical data. During driving of the vehicle, a warning can be issued to the driver on the basis of the notification signal or in response to the notification signal when he is so far away from the next filling station for filling the pressure vessel with fuel, or shortly before this time, to do so that, when the temperature of the fuel is matched to the ambient temperature (either the current ambient temperature or the expected ambient temperature at a later time, wherein this is determined, for example, with reference to weather forecast data), the pressure of the fuel in the pressure vessel lies below the minimum pressure value (wherein, when determining the minimum pressure value, driving to the next filling station after restarting the vehicle after parking is taken into account). This means that a check is made during driving as to whether the vehicle is capable of restarting, that is to say there is a sufficiently high pressure of the fuel after the parking period to move the vehicle, and the vehicle can be driven to the next filling station after restarting without falling below a minimum pressure in the pressure vessel in the event of the vehicle being immediately parked and a parking period (which is so long that complete equalization of the fuel temperature and the ambient temperature has taken place or the duration of which parking period is estimated on the basis of historical data). The minimum pressure is determined in that, below the minimum pressure, the supply pressure for the fuel cell is too low or further extraction of fuel from the pressure vessel can lead to damage to the pressure vessel. The driver can be warned by way of an acoustic and/or optical and/or haptic warning (for example “If you park the vehicle now, it is likely that you will no longer be able to reach a filling station after restarting the vehicle after parking!”) if he/she is too far away from the filling station.
The temperature of the pressure vessel can be taken into account when determining the final pressure value. One advantage of this is that predicting the capability to restart can be carried out more precisely.
Determining the final pressure value of the fuel in the pressure vessel can be carried out on the basis of a characteristic map. As a result, it is possible to ascertain whether the vehicle is capable of restarting after parking with a low level of computational expenditure.
The fuel in the pressure vessel can be heated when the pressure of the fuel in the pressure vessel lies below the minimum pressure value when restarting the vehicle after parking. If the duration of parking was (considerably) longer than the (determined) parking period, the result may be, under unfavorable circumstances in spite of ascertaining or predicting that the vehicle can be restarted, that the pressure of the fuel has dropped below the minimum pressure value. In this case, the fuel can consequently be heated in order to reach a pressure of the fuel which corresponds at least to the minimum pressure value. It is conceivable for the fuel consuming apparatus (for example a fuel cell) to be operated when the tank shut-off valve is blocked by way of fuel being supplied to the fuel consuming apparatus from a buffer store downstream behind the tank shut-off valve. The waste heat from the fuel consuming apparatus can be used to heat the fuel in the pressure vessel. It is also conceivable for a heat exchanger to be supplied with energy by the fuel consuming apparatus and for the heat exchanger to be designed to heat the fuel in the pressure vessel. The energy for heating the fuel in the pressure vessel can come from a high-voltage store.
In particular, the object is also achieved by a pressure vessel system for a vehicle, wherein the pressure vessel system comprises at least one pressure vessel for storing a fuel, a temperature measuring apparatus for measuring the temperature of the fuel in the pressure vessel, a pressure measuring apparatus for measuring the pressure of the fuel in the pressure vessel, and a control device, wherein the control device is designed to determine a final pressure value, in particular when parking the vehicle, wherein the final final pressure value is the expected pressure of the fuel in the pressure vessel after a parking period of the vehicle, and to compare the determined final pressure value with a minimum pressure value for ascertaining whether the vehicle is capable of restarting after the parking period, wherein the control device is further designed to generate a notification signal, in particular when parking the vehicle, when the determined final pressure value lies below the minimum pressure value.
One advantage of this is that it is possible to ascertain whether the vehicle can be restarted as early as before parking of the vehicle, in particular when parking the vehicle. As a result, possible breakdown of the vehicle after parking is prevented.
The pressure vessel system can further comprise a heating apparatus, in particular a heat exchanger, for heating the fuel in the pressure vessel in response to the notification signal being generated if it is possible to reach the minimum pressure value without exceeding a maximum temperature of the fuel in the pressure vessel and without exceeding a maximum pressure of the pressure vessel solely by heating, and the control device is designed to determine the final pressure value again until the final pressure value has reached or exceeded the minimum pressure value. One advantage of this is that it is actively ensured that, when restarting of the vehicle after the parking period or after parking is actually possible on the basis of the existing quantity of fuel or density of fuel, adequate pressure conditions for restarting the vehicle are generated before parking, in particular when parking the vehicle. This prevents breakdown of the vehicle.
The pressure vessel system can further comprise a fuel consuming apparatus which is designed to drive the vehicle and is designed and arranged such that it can be supplied with fuel from the pressure vessel via a fluid line, wherein the pressure vessel system further comprises a buffer store for buffer-storing fuel from the pressure vessel and supplying the fuel consuming apparatus with fuel when the fluid line is blocked. As a result, the fuel consuming apparatus (for example a fuel cell) can be operated when the tank shut-off valve is blocked, that is to say when the fluid line from the pressure vessel is closed. The waste heat from the fuel consuming apparatus can be used to heat the fuel in the pressure vessel. It is also conceivable for a heat exchanger to be supplied with energy by the fuel consuming apparatus and for the heat exchanger to be designed to heat the fuel in the pressure vessel. The energy for heating the fuel in the pressure vessel can come from a high-voltage store.
It is also conceivable for the pressure and the temperature at the time of planned parking of the vehicle to be calculated or determined from the measured pressure and the measured temperature and for these values to be used for determining the final pressure value.
The fuel can be a fuel which is in gaseous form (at standard pressure of 1000 bar and standard temperature of 0° C.), in particular hydrogen. The fuel (for example CNG or H2) can be supplied to a fuel consuming apparatus which is designed to drive the vehicle.
The technology disclosed here relates, inter alia, to a pressure vessel system (compressed hydrogen storage system (=CHS system)) for storing fuel which is in gaseous form under ambient conditions. A pressure vessel of this kind is, in particular, a pressure vessel which is installed or can be installed in a motor vehicle. The pressure vessel can be used in a motor vehicle which is operated, for example, using compressed natural gas (=CNG) or liquefied natural gas (LNG) or using hydrogen. The pressure vessel can be, for example, a cryogenic pressure vessel (=CcH2) or a high-pressure gas vessel (=CGH2). High-pressure gas vessels are designed to permanently store fuel at a maximum operating pressure (also called MOP) of over approximately 350 bar overpressure (=overpressure in comparison to the atmospheric pressure), further preferably of over approximately 500 bar overpressure and particularly preferably of over approximately 700 bar overpressure, essentially at ambient temperatures. A cryogenic pressure vessel is particularly suitable for storing the fuel at temperatures which lie considerably below the operating temperature (meaning the temperature range of the area surrounding the vehicle in which the vehicle is intended to be operated) of the motor vehicle, for example at least 50 Kelvins, preferably at least 100 Kelvins or at least 150 Kelvins below the operating temperature of the motor vehicle (generally approximately −40° C. to approximately +85° C.).
The technology disclosed here will now be explained with reference to the FIGURE.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawing.